Establishment of an irradiation field with a wide range of dose rates for the development of gamma-ray detectors

Dose rates at each position in an irradiation facility have been derived using an ionization chamber. On the other hand, the energy spectrum of gamma-rays at the irradiation positions has not been evaluated. Recently, irradiation tests have been conducted to evaluate the characteristics of gamma-ray detectors, but the energy dependence of some detector materials makes it impossible to accurately evaluate the detector response. Dose evaluations that take into account the energy spectrum at the irradiation location are desired. Furthermore, it is desired that the dose rate in a wide dynamic range from mGy/hr to kGy/hr for the irradiation in the development of gamma-ray detectors. Therefore, the objective of this study is to establish a gamma-ray irradiation field with a wide range of dose rates with energy spectrum evaluated. Dose rates were measured using a high-precision electrometer and an ionization chamber, and the energy spectrum at the irradiation position was evaluated by simulating an irradiation room using a gamma-ray transport Monte Carlo simulation. In the irradiation positions where the gamma-ray source was directly visible, the contamination of scattered gamma-rays in the walls and water phantoms was confirmed. In addition, the contribution of low energy gamma-rays to the energy dependence of the detector was found to be larger at irradiation positions with low dose rates. We were able to establish a gamma-ray irradiation field that reveals the energy spectrum with a wide range of dose rates for the development of gamma-ray detectors.